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Hi,

Just wanted to hear first-hand feedback of ARTEMIS being used on a practical basis. The model has some great features compared to alternatives such as the ease of mesh generation within the TELEMAC suite of models, alongside period-scanning.

However, reading the manual and the limiting requirements for the user determination for the angle of incidence of reflective and liquid boundaries seems like quite a limitation. In practical applications I don't see how this is really possible, especially for complex harbour geometries. Furthermore, an error on the outgoing wave direction at the liquid boundary would surely lead to unwanted reflection throughout the domain leading to vastly wrong results.

I do not completely understand the numerics of the model in this respect, but comparing to something like MIKE-EMS, a simple porosity and sponge layer can be specified without prior knowledge of the wave incidence angle. I'm not sure this is the best approach either and why one approach would be implemented over the other.

In any case, is this really a major limitation of the model (does it have a great influence on the results) and has anyone got advice to applying the model in practical applications where the angles cannot be reliably determined?

Cheers,
Toby

Hello Toby,

I guess the ARTEMIS manual has not been updated for *quite* some time. All of the above mentioned limitations have been addressed over the time. Reflective incidence angle has, since many years, an option to be automatically derived and I can't recall "unwanted reflection at the liquid boundary" being a matter of serious, if any, trouble.

If the above are your only concerns, then by all means, give it a try. There are may other upgrades/features that are not documented at all. FYI, I've used ARTEMIS in 10+ real case scenarios.

Regards,
Costas

Hi Costas,

Thanks for the response. It’s encouraging to hear that many of my concerns have likely been addressed - it’s just unfortunate that the user manual has not been updated to describe them.

I need to setup a model is a short amount of time and haven’t had a chance to play with the model too much or delve into these hidden features. I was wondering if you could possibly answer the following questions for me please:

1. You mentioned that the required reflective incidence angle can be automatically calculated (I believe this is TETAP. Does this require putting a dummy value in the BORH subroutine and simply activating a keyword? Furthermore, does the user still need to specify the phase angle ALPHAP and if so do you have any recommendations for estimating this?

2. To set up an incident wave boundary with absorbing properties I assume that the boundary type needs to be type LIHBOR=1 /KINC? Does the user still have to manually provide the incident wave phase. It seems that the user manual stated that this feature was removed but it would be nice to have as long as the limitations on its use were explicitly mentioned. For simple boundaries orientated perpendicular to the wave direction this is not of concern but it would be great to use radial boundaries to accommodate various incident directions in the one grid.

Appreciate your help. Doesn’t look like the ARTEMIS sub forum gets much attention :)

Regards,
Toby

Hello Toby,
Have a look at the .dico file in the ARTEMIS sources. There you can find a brief description of all keywords that can give you a hint of the available options.
1. The keyword you need is AUTOMATIC TETAP CALCULATION. ALPHAP does not necessarily be defined. I rarely bother to define it.
2. Do know that boundary conditions can now be set in the CLI file. Regarding ALFAP and TETAP, read the following post(#32149). I would advise to read the whole thread to get some pointers regarding undocumented features.
Also coupling with TELEMAC was a much needed upgrade that you look into. Have a look at the 2018 TUC proceedings for a full documentation regarding major ARTEMIS upgrades.
Best Regards,
Costas

Dear Costas,

Managed to get it up and running without a problem - just took me a while to figure out that you could specify the boundary condition values directly in the cli file. After that everything was quite smooth and straight forward - much better experience than some other mild-slope models I've used.

I just wanted to ask about the timestep parameter. There is no mention in the user manual regarding timestep requirements. Is the model conditionally stable or does the default timestep need to be adjusted occasionally? Seemed to work for me at the default setting over a wide range of wavelengths.

Thanks

Hello Toby,
No timestepping for ARTEMIS. You just need define some solution convergence parameters like:These control speed of convergence vs accuracy of results. Thus, convergence is not always guaranteed.

Bear in mind the wavelength/mesh resolution ratio. Too small ratio and the model will not converge. The minimum ratio is given at the manual (~7 if I recall correctly).
Costas

Hi Costas,

Big help - thanks for that. One other question. Is there anyway to have multiple wave generation boundaries with different orientations while maintaining the automatic phase calculation? Is this just a matter of specifying multiple incident wave angles for each of the wave boundaries?

Also, are you aware if there is any way to use circular boundaries to reduce the mesh size without modifying the source? I assume this is likely not possible given that the incident wave angle is specified relative to the the boundary itself (i.e. the incident angle would change for each segment)

Thanks,

If I recall correctly you can have multiple wave generation boundaries as long as wave they are not opposing each other and wave tries to exit through an incident wave boundary. Outgoing wave will probably get reflected back.
This limitation also applies to circular boundaries as well. Other that that, I can't think any reason why they should not work. I haven't tried circular myself but I have tried trapezium-like and apart some reflections, it worked fine.
Costas

Hi Costas,

I've attempted to run a case with two differently orientated wave boundaries but am observing some strange wave shadowing issues. The model is simple case of monochromatic waves with unit wave heights. I have attached the CAS, CLI and BOTTOM files for reference. The southern and western boundaries of the domain are LIHBOR = = 1 (Incident Wave). All other model boundaries are of type LIHBOR = 4 (Free exit). Automatic calculation of TETAP is enabled.

As you can see in the attached wave height plot there is an area projecting from the corner of the two incident wave boundaries at the south-west of the model domain when the wave height is significantly lower than the incident wave height. Have you run into this issue before and do you know the correct way to resolve it?


Thanks again,
Toby

Hi Toby,
Can you try treating the offshore boundary as one, i.e. no split at the corner. Cases where this issue occurred to me is when shoaling takes place right from the boundary. Try increasing the depth/water elevation and/or decrease wave period to investigate this possibility.
Best Regards,
Costas